Homebrew A 4 To 1 Balun
Many modern HF transceivers come
fully equipped with built in tuners. While these tuners are great
for changing bands, the manufacturers left out a very important
accessory; the 4 to 1 balun. With out a balun the transceiver can
only feed an antenna which uses coaxial cable. While this may be
satisfactory for some operators, this is a real problem for those
of us who prefer the super low loss ladder line. The only other
alternative is to buy an external tuner with a built-in balun
which is really absurd after spending the additional money to
have one built into the radio. Fortunately, a 4 to 1 balun can be
easily home brewed as illustrated in Figures 1 and 2.
Figure 1 shows a bifilar winding
on a toroid. The toroid should be type 2 (red) material and can
be any of the following sizes but the number of bifilar turns
should be adjusted accordingly:
NUMBER OF TURNS
The exact number of turns is not
critical but the numbers listed in the preceding table should
yield optimum results. It is possible to exceed the power ratings
listed above but the performance of the balun may be degraded
during high SWR causing heating of the core.
Toroids of this type are available
from Palomar Engineers, P.O. Box 462222, Escondido, CA 92046
(1-800-883-7020). If enough inquires are made, the author will
make a limited number of toroids available at RASON meetings for
those who hate mail order. The author will even wind the toroid
for the faint of heart.
The balun should be housed in a
suitable metal enclosure such as those available at Radio Shack.
Use a SO239 or BNC connector for the unbalanced input. Nylon
binding posts such as RS 274-662 work just fine for the balanced